Soft Pulsing RF Signal Control for Plasma Impedance Stability
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Solution Overview
Problem
In plasma processing systems, controlling the etching or deposition process is challenging due to instability caused by sudden changes in plasma impedance, which leads to loss of control over the etching or deposition process on wafers.
Innovation Solution
The method involves generating a radio frequency (RF) signal with a statistical measure that has a positive or negative slope, gradually increasing or decreasing the root mean square (RMS) value over time to control the rate of change of plasma impedance, thereby stabilizing the process and maintaining control over etching or deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an RF signal with sudden changes in RMS value is supplied to the plasma chamber, then the etching or deposition process can be initiated or stopped quickly, but plasma impedance instability occurs causing loss of control
Solution Approach 1:
The patent applies dynamics by making the RF signal characteristics variable rather than fixed. The system dynamically adjusts the RMS value of the RF signal over time using controlled transitions (ramps) rather than abrupt changes. This dynamic approach allows the system to respond quickly when needed while maintaining plasma stability during transitions, resolving the contradiction between speed and reliability.
Solution Approach 2:
The patent changes the parameter of RF signal RMS value from constant to variable with controlled transitions. By introducing ramp-up and ramp-down periods where the RMS value changes gradually rather than instantly, the system achieves both quick response capability and plasma impedance stability. This parameter change approach directly addresses the technical contradiction.
2Loss of time
If the RF signal RMS value changes abruptly, then process control transitions are faster, but the rate of change of plasma impedance increases causing instability
Solution Approach 1:
The patent applies periodic action by structuring the RF signal delivery in distinct phases: ramp-up period, steady-state period, and ramp-down period. This periodic structure with controlled transition phases allows the system to achieve fast overall cycle times while maintaining plasma stability during each phase, resolving the contradiction between transition speed and impedance stability.
3Reliability
If the rate of change of plasma impedance is reduced by using gradual RMS transitions, then plasma stability is improved, but the response time of the etching or deposition process increases
Solution Approach 1:
The patent applies partial action by using moderate ramp rates rather than extremely gradual changes. The ramp-up and ramp-down periods are optimized to provide sufficient plasma stability while keeping the transition time reasonable. This partial approach balances the competing requirements of stability and response time, avoiding the extremes of either very fast transitions (causing instability) or very slow transitions (causing excessive delay).
Data Source
AI summary
Systems and methods for soft pulsing are described. One of the systems includes a master radiofrequency (RF) generator for generating a first portion of a master RF signal during a first state and a second portion of the master RF signal during a second state. The master RF signal is a sinusoidal signal. The system further includes an impedance matching circuit coupled to the master RF generator via an RF cable to modify the master RF signal to generate a modified RF signal and a plasma chamber coupled to the impedance matching circuit via an RF transmission line. The plasma chamber is used for generating plasma based on the modified RF signal. A statistical measure of the first portion has a positive or a negative slope.